Page 25 - Algae

8 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 1.7 Simple filament of FIGURE 1.8 Simple filament FIGURE 1.9 Simple filament
Oscillatoria sp. of Spirogyra sp. of Ulothrix variabilis.

Vegetative and asexual modes allow stability of an adapted genotype within a species from a gen-
eration to the next. Both modes provide a fast and economical means of increasing the number of
individuals while restricting genetic variability. Sexual mode involves plasmogamy (union of
cells), karyogamy (union of nuclei), chromosome/gene association, and meiosis, resulting in
genetic recombination. Sexual reproduction allows variation but is more costly because of the
waste of gametes that fail to mate.

VEGETATIVE AND ASEXUAL REPRODUCTION
Binary Fission or Cellular Bisection
It is the simplest form of reproduction; the parent organism divides into two equal parts, each
having the same hereditary information as the parent. In unicellular algae, cell division may be
longitudinal as in Euglena (Euglenophyta) (Figure 1.16) or transverse. The growth of the popu-
lation follows a typical curve consisting of a lag phase, an exponential or log phase, and a stationary
or plateau phase, where increase in density is leveled off (see Chapter 6). In multicellular algae or in
algal colonies this process eventually leads to the growth of the individual.